Catenary
The overhead wire system that delivers electric current to a train through a pantograph in contact with the wire.
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Catenary is the overhead electrical contact line used to power trains on most of the world's electrified mainlines. The term technically refers to the mathematical curve a hanging wire forms under gravity, but in railway usage it has come to describe the whole assembly: the contact wire that the pantograph rubs against, the messenger (or catenary) wire above it that supports the contact wire at a constant height, and the droppers that connect the two. Together they keep the contact wire level even as it spans the gap between support masts.
The masts themselves — often called portals when they bridge multiple tracks — carry the wire above the running rails at a height typically between 4.7 and 6.5 metres, depending on the country and the loading gauge. Voltage and current type vary widely by network: 25 kV 50 Hz AC is the modern continental and high-speed standard, 15 kV 16.7 Hz AC covers most of German-speaking Europe, 3 kV DC is the legacy Italian and Belgian system, and 1500 V DC is common in the Netherlands, France, and parts of Australia.
For photographers, catenary is the constant compositional challenge of electrified lines: it cuts across the sky behind the train, fights with clean roofline silhouettes, and is nearly impossible to retouch out without leaving artifacts. Many railfans deliberately frame low — shooting up from a sloped embankment or from the side rather than head-on — to push the wires out of the most important part of the frame.